Ionis Pharmaceuticals (IONS) Stock: Shares Plunge as Phase 3 Heart Trial Misses Goal

TLDR

• Ionis shares tumble after eplontersen misses key Phase 3 heart trial goal today

• IONS sinks in pre-market after ATTR-CM study misses main Phase 3 efficacy goal

  

• Eplontersen shows subgroup signal but fails to prove broad trial benefit in study

• Stabilizer use weighs on treatment effect in Ionis-AstraZeneca heart study data

• Ionis and AstraZeneca will present full CARDIO-TTRansform data at ESC in August

Ionis Pharmaceuticals (IONS) stock dropped sharply after its key Phase 3 heart disease trial missed its main goal. The stock closed 2.17% lower at $84.46, then fell 20.38% to $67.25 in pre-market trading. The setback hit sentiment because the trial tested eplontersen in a major heart-related amyloidosis population.

Ionis Pharmaceuticals, Inc., IONS

Ionis Pharmaceuticals Stock Falls After Trial Setback

Ionis and AstraZeneca reported that CARDIO-TTRansform failed to meet its primary efficacy endpoint. The trial tested eplontersen against placebo in patients with transthyretin-mediated amyloid cardiomyopathy. The main endpoint tracked cardiovascular death and recurrent cardiovascular clinical events through Week 140.

The companies said eplontersen did not deliver a statistically significant benefit in the full patient group. Standard care also shaped the result because many patients already used stabilizer therapy. Therefore, the added effect of eplontersen appeared limited in the broader trial population.

Ionis Pharmaceuticals (IONS) stock reacted quickly to the failed primary endpoint. The pre-market plunge showed concern around the treatment’s commercial path in ATTR-CM. However, the companies said several secondary, imaging, and biomarker results favored eplontersen.

Eplontersen Shows Mixed Results In ATTR-CM Study

The trial showed a different signal in patients who used eplontersen without stabilizer therapy. In that subgroup, eplontersen showed a nominally significant hazard ratio of 0.71. Still, patients using stabilizers at baseline showed no treatment effect.

Eplontersen produced large and sustained reductions in transthyretin protein. That result matched the expected profile of RNA-targeted silencer medicines. The companies also reported a favorable safety profile consistent with earlier eplontersen data.

CARDIO-TTRansform enrolled 1,432 adults across 130 sites in 20 countries. The study included patients with wild-type or hereditary ATTR-CM. Participants received eplontersen 45 mg or placebo by subcutaneous injection every four weeks.

Ionis And AstraZeneca Plan Further Data Review

ATTR-CM causes misfolded transthyretin protein to build up in the heart. Over time, this buildup disrupts heart structure and weakens normal pumping function. Patients often face shortness of breath, swelling, weakness, dizziness, palpitations, and fatigue.

The disease can come from inherited mutations or develop with age. Ionis said the trial reflected a changing treatment landscape with greater stabilizer use. This context may help explain the weaker result in the overall study population.

Ionis and AstraZeneca will continue reviewing the full CARDIO-TTRansform data set. The companies plan to share results at the European Society of Cardiology Congress in August 2026. Meanwhile, Ionis said its broader pipeline and launched medicines remain central to its long-term plan.

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